1. Field of the Invention
This invention relates to a fuel injection device in a deisel engine, and more particularly to improvements in a fuel injection device in a diesel engine, suitable for use in a motor vehicle diesel engine provided with an electromagnetic spill type fuel injection pump, wherein a fuel injection quantity is controlled by a high pressure electromagnetic valve which is on-off controlled in accordance with engine operating conditions.
2. Description of the Prior Art
Because of developments in digital control techniques in recent years, a so-called electronically controlled diesel engine, wherein a fuel injection pump in a diesel engine is electronically controlled, has been commercialized.
There are various methods of electronically controlling the fuel injection pump, one of which is a method using an electromagnetic spill type fuel injection pump, wherein spill of fuel in the fuel injection pump is controlled by an electromagnetic valve. In this electromagnetic spill type fuel injection pump, upon the fuel injection quantity reaching a target valve, a spill port is released by a high pressure electromagnetic valve to control the fuel feed under the pressure, thus controlling the fuel injection quantity.
When a diesel engine, wherein the fuel injection quantity is controlled by a high pressure electromagnetic valve, uses a normally closed type electromagnetic valve as a high pressure electromagnetic valve, the disconnection of a solenoid in the electromagnetic valve or the blocking of a path in the electromagnetic valve by extraneous matters results in a full quantity injection condition of the fuel injection pump, thus disabling its control and causing an overrun of engine speed. Furthermore, when a normally open electromagnetic valve is used, trouble in a control circuit, a short-circuit between a wire harness of the electromagnetic valve and a battery or the continuous passing of current through the solenoid, causes the full quantity injection conditions, resulting in the inability control the fuel injection quantity and the occurence of an overrun of engine speed as well.
To obviate the above-described disadvantages, Japanese Patent Laid-Open No. 47630/1981 discloses that, when an abnormal increase in engine speed is detected, a fuel cut solenoid is closed, thereby stopping the fuel supply.
Furthermore, in Japanese Utility Model Application No. 13777/1984, the applicant discloses that, when a difference between a target engine speed and an actual engine speed exceeds a predetermined value, the fuel cut solenoid is closed in order to stop the fuel supply.
In all of these conventional cases, however, a fuel cut solenoid separate from the electromagnetic spill valve is provided, such that when an abnormality in the engine speed is detected, the fuel supply is cut by the fuel cut solenoid. Then electromagetic valve itself is not protected and a power source voltage is applied to the electromagnetic spill valve due to a trouble in the electromagnetic valve driving circuit, a wire harness or the like. When current continues to flow through the electromagnetic spill valve, the valve falters. Furthermore, when an abnormality is detected from the engine speed, it is detected indirectly, resulting in too slow on engine response.
Alternatively, U.S. Pat. No. 4,491,112 discloses a failsafe system for an engine control servomotor, wherein a servomotor command signal is compared with a feedback signal from the servomotor, and, when a difference therebetween is higher than a preset value for more than a preset time period, the servomotor is shut down. However, this invention does not attempt to protect the high pressure electromagnetic valve, as does the present invention.